This study is to examine the change of fasting insulin, glucose, insulin sensitivity and related traits in response to the six month treatment of omega-3 fatty acids, including fish oil and flaxseed oil, in Chinese type 2 diabetic patients. Corn oil, rich in omega-6 fatty acids, will be selected as a controlled oil. The investigators hypothesize that omega-3 fatty acids could improve insulin sensitivity and glucose metabolism in Chinese type 2 diabetic patients.